1. Field of the Invention
The present invention relates to a media library system having a storehouse for storing a large number of recording media such as optical disks, magnetic disks, magnetic tapes, etc., which carries out the-exchange of the recording media and the data access to the recording media automatically.
2. Description of the Background Art
The optical disk device is a storage device for exchangeably storing optical disk media, where each optical disk medium is either a type of 90 mm diameter having several hundred MB recording capacity or a type of 130 mm diameter having approximately 1 GB recording capacity, such that unlimited amount of recording capacity can be realized in principle by the exchange of the optical disk media.
In recent years, there has been a development of an optical disk library system which realizes the recording capacity of 1 TB level by carrying out the exchange of the optical disk media automatically, by taking an advantage of such an optical disk device. This optical disk library system has a schematic configuration as shown in FIG. 1, in which a standard type cartridge 1 containing one optical disk medium is mounted onto a disk drive 2 to carry out data read/write with respect to the optical disk medium contained in the cartridge 1, and an arbitrary cartridge 1 stored in a storage cell 3a of a storehouse 3 can be exchanged with the cartridge 1 in the disk drive 2 by being conveyed by a robotic hand 4 of an automatic disk handling mechanism.
Normally, in a case of exchanging the cartridges 1, as shown in FIG. 1, the cartridge 1 taken out from the disk drive 2 is conveyed over to the prescribed storage cell 3a of the storehouse 3 by the robotic hand 4 as indicated by an arrow 1, and then the robotic hand 4 is moved over to the storage cell 3a of a next cartridge 1 as indicated by an arrow 2, and finally this next cartridge 1 is conveyed over to the disk drive 2 as indicated by an arrow 3.
However, this manner of exchanging the cartridges 1 requires to return the cartridge 1 mounted on the disk drive 2 to the prescribed position first, and then convey the new cartridge 1 stored in the storehouse 3 to the disk drive 2, so that an average access time of the optical disk has been as much as ten to twenty seconds in a conventional optical disk library system.
Now, in the optical disk library system, there is a possibility for a need to continuously reproduce data which are recorded in division on a plurality of recording media. In order to cope with this situation, there is a proposition for a provision as shown in FIG. 2 to provide two escape cells 5 for temporarily storing cartridges 1 in a vicinity of the disk drive 2 such that the cartridge 1 to be accessed next can be standing by in advance in these escape cells 5 to shorten the exchange time of each cartridge 1.
In this case, the cartridge 1 to be accessed next is moved from the storage cell 3a to one of the escape cells 5 by the robotic hand 4 in advance as indicated by arrows 1 and 2, and when the data read/write with respect to the previous cartridge 1 is finished, the finished cartridge 1 is temporarily stored in the other one of the escape cells 5 as indicated by arrows 3 and 4. Then, the next cartridge 1 in one of the escape cells 5 is mounted on the disk drive 2 to restart the data read/write as indicated by arrows 5 and 6. After that, the previous cartridge 1 temporarily stored in the other one of the escape cells 5 is returned to the prescribed storage cell 3a of the storehouse 3 as indicated by arrows 7, 8 and 3.
However, according to this proposition, the advance moving of the cartridge 1 to the escape cells 5 is going to be carried out even for those cartridges 1 which have little influence on the access time as they are already located in a vicinity of the disk drive 2, so that the average moving distance of the robotic hand 4 is going to be increased beyond what is absolutely necessary. In particular, in a case very frequent movements of the robotic hand 4 is required as in a case of using a plurality of disk drives 2 with respect to a single storehouse 3, it is even possible for this increased robotic hand moving distance to cause the lowering of the cartridge exchange performance itself.